[kirkstone] ref-manual: document image-specific variant of INCOMPATIBLE_LICENSE

From: Michael Opdenacker <michael.opdenacker@bootlin.com>

This has been around without being properly documented since 2019 (!!!),
and is nowadays the preferred method for enforcing license restrictions,
especially since meta-gplv2 is officially obsolete.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
---
 documentation/ref-manual/images.rst    | 16 +++++++++-------
 documentation/ref-manual/variables.rst | 11 ++++++++++-
 2 files changed, 19 insertions(+), 8 deletions(-)

Just in case, dunfell can get this too, with old-style override syntax.

Alex

On Mon, 31 Jul 2023 at 19:58, Michael Opdenacker via
lists.yoctoproject.org
<michael.opdenacker=bootlin.com@lists.yoctoproject.org> wrote:
>
> From: Michael Opdenacker <michael.opdenacker@bootlin.com>
>
> This has been around without being properly documented since 2019 (!!!),
> and is nowadays the preferred method for enforcing license restrictions,
> especially since meta-gplv2 is officially obsolete.
>
> Signed-off-by: Alexander Kanavin <alex@linutronix.de>
> Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
> ---
>  documentation/ref-manual/images.rst    | 16 +++++++++-------
>  documentation/ref-manual/variables.rst | 11 ++++++++++-
>  2 files changed, 19 insertions(+), 8 deletions(-)
>
> diff --git a/documentation/ref-manual/images.rst b/documentation/ref-manual/images.rst
> index 31fb567687..33e5b53d9f 100644
> --- a/documentation/ref-manual/images.rst
> +++ b/documentation/ref-manual/images.rst
> @@ -14,15 +14,17 @@ image you want.
>     Building an image without GNU General Public License Version 3
>     (GPLv3), GNU Lesser General Public License Version 3 (LGPLv3), and
>     the GNU Affero General Public License Version 3 (AGPL-3.0) components
> -   is only supported for minimal and base images. Furthermore, if you
> -   are going to build an image using non-GPLv3 and similarly licensed
> -   components, you must make the following changes in the ``local.conf``
> -   file before using the BitBake command to build the minimal or base
> -   image::
> +   is only tested for core-image-minimal image. Furthermore, if you would like to
> +   build an image and verify that it does not include GPLv3 and similarly licensed
> +   components, you must make the following changes in the image recipe
> +   file before using the BitBake command to build the image:
>
> -           1. Comment out the EXTRA_IMAGE_FEATURES line
> -           2. Set INCOMPATIBLE_LICENSE = "GPL-3.0* LGPL-3.0* AGPL-3.0*"
> +       INCOMPATIBLE_LICENSE = "GPL-3.0* LGPL-3.0*"
>
> +   Alternatively, you can adjust ``local.conf`` file, repeating and adjusting the line
> +   for all images where the license restriction must apply:
> +
> +       INCOMPATIBLE_LICENSE:pn-your-image-name = "GPL-3.0* LGPL-3.0*"
>
>  From within the ``poky`` Git repository, you can use the following
>  command to display the list of directories within the :term:`Source Directory`
> diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
> index 9aab6e0709..88b27492c7 100644
> --- a/documentation/ref-manual/variables.rst
> +++ b/documentation/ref-manual/variables.rst
> @@ -3547,9 +3547,18 @@ system and gives an overview of their function and contents.
>     :term:`INCOMPATIBLE_LICENSE`
>        Specifies a space-separated list of license names (as they would
>        appear in :term:`LICENSE`) that should be excluded
> -      from the build. Recipes that provide no alternatives to listed
> +      from the build (if set globally), or from an image (if set locally
> +      in an image recipe).
> +
> +      When the variable is set globally, recipes that provide no alternatives to listed
>        incompatible licenses are not built. Packages that are individually
>        licensed with the specified incompatible licenses will be deleted.
> +      Most of the time this does not allow a feasible build (because it becomes impossible
> +      to satisfy build time dependencies), so the recommended way to
> +      implement license restrictions is to set the variable in specific
> +      image recipes where the restrictions must apply. That way there
> +      are no build time restrictions, but the license check is still
> +      performed when the image's filesystem is assembled from packages.
>
>        There is some support for wildcards in this variable's value,
>        however it is restricted to specific licenses. Currently only
> --
> 2.34.1
>
>
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On 31.07.23 at 20:10, Alexander Kanavin wrote:
> Just in case, dunfell can get this too, with old-style override syntax.
>
> Alex


Done. I also removed the mention of meta-gpl2 which is still supported 
with Dunfell.
Thanks!
Michael.